1. Field of the Invention
The present invention relates to a stereolithography apparatus for creating a three-dimensional object by irradiating a predetermined photo-curable resin with light such as laser light. More particularly, the invention relates to a stereolithography apparatus suitable for the creation of an object having a size on the order of microns.
2. Description of the Background Art
A stereolithography technique is already known in the art such that cross-sectional shape data representing the shapes of a plurality of cross-sections into which a three-dimensional object is sliced from bottom to top at predetermined spacing is previously generated based on three-dimensional shape data (e.g., CAD data) representing the three-dimensional object, and planar resin layers representing the respective sliced cross-sections are successively formed based on the cross-sectional shape data by curing a photo-curable resin whereas one planar resin layer is stacked on top of another each time the planar resin layer is formed, whereby a model corresponding to the three-dimensional object is created. A stereolithography apparatus for implementing the stereolithography technique is also known in the art. The stereolithography technique and apparatus are disclosed, for example, in Japanese Patent Application Laid-Open No. 2004-249508, Japanese Patent Application Laid-Open No. 2004-223789, and Japanese Patent No. 3294833. A variety of methods of modeling have been proposed. These methods are based on a generally common technique in creating a model by repeating the formation of a resin layer and the stacking of the resin layer on top of another, the formation of the resin layer being accomplished by irradiating an uncured photo-curable resin within an irradiation area determined by the cross-sectional shape data with exposure light such as, for example, laser light.
The stereolithography technique, in which a model can be relatively easily created from design data for embodying the model, has been conventionally used in prototyping a variety of products. In recent years, models to be created have been reduced in size, and studies for application of the stereolithography technique to so-called micromachining have been conducted actively.
For micromachining, the required overall size of the models is up to about hundreds of micrometers, and the components thereof are accordingly required to be formed to have a size at least one order of magnitude smaller than that of the models. To achieve this, it is necessary to attain modeling accuracy of not greater than tens of micrometers, more preferably not greater than about 10 to about 20 micrometers.
In the stereolithography apparatus, the modeling accuracy is considered to principally depend on the accuracy of the thickness of each of the stacked resin layers, and an exposure resolution. For the former, it is necessary to increase the accuracy of the process of forming the resin layers. For the latter, it is necessary to increase the accuracy of the process of irradiation with exposure light. From the viewpoint of the former, it is necessary that a mechanism responsible for supplying resin to a modeling surface and a mechanism responsible for smoothing the resin are close to the modeling surface. From the viewpoint of the latter, on the other hand, a distance between a position from which the exposure light comes and the modeling surface is preferably as short as possible because of the problem of the stability of the exposure light and the like. Also, for the latter, an irradiation element (or irradiation optical system) for irradiation with the exposure light can be said to be preferably fixed in view of the stability of the exposure light.
The exposure resolution is determined depending on the focusing of the exposure light. It is hence necessary that focus is always maintained on the surface of a resin layer being exposed to light during the modeling. However, as more resin layers are stacked, more deviations from the setting of the thickness of the layers are accumulated, which might result in no focus achieved on the surface of the resin layers. In some cases, no focus is achieved on the surface of the resin layers because of the height variations or unevenness of a base surface during the modeling. If such an out-of-focus condition occurs but cannot be detected in the course of the modeling, a judgment as to whether the model is good or not has to be made directly from the model itself after the model is actually completed. This hinders improvements in yield and in productivity.
Japanese Patent Application Laid-Open No. 2004-249508 discloses a stereolithography apparatus in which an exposure light source is fixed whereas a stage is moved, but provides no disclosure about the increase in the accuracy of the thickness of resin to be cured.
This apparatus has an optical unit for achieving focus, and a detector provided in the optical unit detects a reflection of light emitted from a light source provided in the optical unit, whereby focusing is adjusted. With such an arrangement, however, it is difficult to achieve focus with high accuracy because no judgment is made as to whether the focusing of the exposure light itself for actual use in exposure is good or not.
Japanese Patent Application Laid-Open No. 2004-223789 discloses a stereolithography apparatus having an optical system for scanning with exposure light by means of a galvanometer mirror. This apparatus further includes a beam splitter disposed in some midportion of an irradiation optical system for the exposure light, an imaging camera disposed in the path of light split by the beam splitter, and an illumination light source for observation disposed under a substrate serving as a modeling stage. However, there is no disclosure about the increase in the accuracy of the thickness of a resin layer.
In this stereolithography apparatus, when the illumination light source emits illumination light during the modeling, the light transmitted through a glass substrate and a model is introduced by the beam splitter toward the imaging camera disposed in the split light path, and the modeling condition can be recognized by viewing the resultant image. Such an arrangement, however, presents problems in that the illumination light source is essential and in that the materials of the stage and the model are limited to those transparent to the illumination light.
Japanese Patent No. 3294833 discloses an apparatus of a so-called free surface type which includes a tank previously filled with a resin and which creates a model by repeating the exposure of the surface of the liquid resin to light and the downward movement of a stage. In this apparatus, exposure to light is achieved by scanning by means of an irradiation element. There is a large separation between the irradiation element and the liquid surface irradiated with light because an element for smoothing the resin is disposed between the irradiation element and the liquid surface.
This apparatus includes an element for detecting the liquid surface, but does not include an element for observing the modeling condition.